1. Field of the Invention
The present invention relates to a light-sensitive resin (or photoresist) composition and a metal image-forming material using the same. More particularly, it relates to a light-sensitive resin composition containing an ethylenically unsaturated compound having at least two terminal ethylenically unsaturated groups, a photo-addition polymerization initiator, and an organic binder containing a repeating unit derived from a specific aralkyl acrylate or aralkyl methacrylate and a repeating unit derived from acrylic acid or methacrylic acid, capable of being dissolved or swollen in an alkaline aqueous solution, and to a metal image-forming material using the same.
2. Description of the Prior Art
Heretofore, lithographic films of an ultra-high-contrasty silver halide emulsion have generally been mainly used in an image-forming process suitable for half dot line working. While the invention with ordinary silver halide emulsions is to reproduce a halftone gradation, the intention with lithographic films for the graphic arts is to form images of transparent areas and blackened opaque areas alone. Therefore, of the characteristics which lithographic films possess, it is necessary in particular that the images obtained have a clear outline and provide an accurate line width. Actually, however, these characteristics are obtained only with difficulty for the following reasons in practical image formation using lithographic films.
Firstly, lithographic films have a width of from the base optical density to the maximum optical density in the characteristic curve, although they should desirably form transparent areas and blackened areas which are distinct and discriminatable from each other. This width in the characteristic curve results in fringe being formed around the images.
Secondly, size of the image areas tends to expand and grow as the developing time is lengthened, since development of lithographic films is based on infectious development. Therefore, stopping development is difficult, and the line width tends to change. Also, infectious development not only influences the formation of fringe but also makes precise control of development difficult.
Further, in order to acquire workers, too, it is desired and expected in this field to change the working location to a room bright enough such that presensitized plates are exposed. Since silver is a resource which is limited, from the viewpoint of effectively using restricted resources such as silver, too, it is eagerly desired to solve the above-described problems using non-silver salt light-sensitive materials. On considering the above from a market standpoint, several products utilizing organic compounds have recently been marketed commercially. For example, diazo type SG positive films (made by Scott Co.), diazo type contact films (made by Oce Co.), photochromic films (made by Dai-Nippon Printing Co., Ltd.), and the like are available. However, these films have at least two defects. One defect is that image areas having an optical density as high as 3.5 or more are difficult to form. The other defect is that dot etching, which is necessary as films for contact, is difficult.
As an image-forming process for possibly attaining such objects, Japanese patent application (OPI) No. 139720/75 (corresponding to U.S. patent application Serial No. 571,817, filed Apr. 25, 1975 now U.S. Pat. No. 4,008,084) describes an image-recording material comprising a transparent support having provided thereon a thin layer of an aluminum-iron alloy and a light-sensitive resin layer in this order. Furthermore, Japanese Patent Publication No. 14161/75, Japanese patent application (OPI) No. 65928/73 (corresponding to U.S. patent application Ser. No. 205,861, filed Dec. 8, 1971), 65927/73 (corresponding to U.S. patent application Ser. No. 205,860, filed Dec. 8, 1971) and 2925/75 describe a process for forming metal images by using an image-forming material comprising a support having provided thereon an opaque thin layer of a metal such as tellurium, molybdenum, polonium, cobalt, zinc, aluminum, copper, nickel, iron, tin, vanadium, germanium, silver or silver emulsion and, further, a light-sensitive resin layer (as described hereinafter) thereon, subjecting the image-forming material to an image-wise exposure, developing the light-sensitive resin layer, and etching the uncovered metal layer with a second solution; and a process for forming images by conducting, after image-wise exposure, a mono-bath development processing using an alkaline developer containing sodium hypochlorite to thereby selectively remove the resin layer and simultaneously or substantially simultaneously etching the metal layer. The latter process is superior to a conventional two-bath development from the standpoint of shortening the working steps.
When an aluminum layer or an aluminum-iron alloy layer is used as the metal layer from the viewpoint of minimizing environmental pollution, an alkaline solution or an acidic solution may be used as an etching solution. However, in the etching process utilizing this mono-bath development, an alkaline etching solution is advantageous, since some photo-polymerizable light-sensitive resins require alkaline development after exposure. Further, with reprographic copying materials for producing printed circuit plates or for optically producing printing plates, too, an alkaline water developer is advantageous from the viewpoint of preventing environmental pollution as compared with a developer using an organic solvent, and provides the advantages of low cost, good stability and simple after-treatment. Further, dissolved copying materials can be separated from the used developer by acidifying and subsequent filtration.
Photo-polymerizable copying layers which can be developed with an alkaline aqueous solution are known. The desired properties can generally be obtained by adding a binder which is soluble or at least swellable in an alkaline aqueous medium. For this purpose, homopolymers or copolymers having groups whose solubility in water/alkali medium is controlled such as a carboxylic acid group, a carboxylic acid anhydride group or a phenolic or alcoholic hydroxy group or the like are used. However, these alkali-developable, photo-polymerizable light-sensitive resin compositions for forming a protective layer have the defect that hardened resist areas tend to have inferior chemical resistance, particularly, alkali resistance. Therefore, in the production of printed circuit plates, processing solutions such as an etching solution and a plating solution are limited. In addition, in the above-described process for forming metal images for use as films for contact, reduction of dot images is particularly disadvantageously conducted. Because, a much stronger reducer than a developer must be used when an alkaline reducer is used, in order to thin the dots of the dot images formed by the development, by etching metal in a short time utilizing side etching. Therefore, when the resist layer does not possess sufficient alkali resistance, pinholes will be formed in the dots or, in the extreme case, the dots themselves will be etched away.
Furthermore, the kind of binder used greatly influences the developability, sensitivity and mechanical strength of a resist film.